Technical Abstract:
Host-plant resistance is economic and highly effective for root-knot nematode (RKN) Meloidogyne incognita control in cotton Gossypium hirsutum. Nematode resistance can protect cotton plants from direct injury due to nematode infection, and can protect against the root-knot nematode-Fusarium wilt disease complex. In addition, resistance in cotton suppresses soil nematode population densities, thereby benefiting other susceptible crops grown in rotation. Recently, nematode resistance gene mapping has revealed relationships between resistance sources and linked molecular markers for use in genetic improvement of cotton. Markers are important tools for incorporating resistance genes into elite cultivars by indirect selection. Microsatellite markers (SSR) linked to RKN resistance in G. hirsutum Acala NemX were identified using segregating progenies and recombinant inbred lines from intraspecific crosses and an interspecific cross with G. barbadense Pima S-7. Informative SSR were mapped on the above populations, including one co-dominant SSR marker CIR316 tightly linked (2.1 to 3.3 cM) to a major resistance gene (rkn1). Additional markers allowed the rkn1 gene to be mapped to cotton chromosome 11. Other markers linked to rkn1 were developed from AFLP screening and converted to CAPS and SNP markers for high throughput screening. Subsequently, a similar location of the major resistance determinant present in the Auburn source of RKN resistance was reported, and additional non-linked minor QTL for resistance identified. Higher levels of resistance in cotton were obtained by transgressive segregation with factors contributed by susceptible parents in intraspecific and interspecific crosses. These gene relationships and use of markers for cotton improvement are discussed.